Improved measurement of $CP$ violation parameters in $B^0_s\to J/\psi K^{+}K^{-}$ decays in the vicinity of the $\phi(1020)$ resonance

TL;DR

This paper presents the most precise measurements to date of $CP$ violation parameters in $B^0_s o J/ heta$ decays near the $(1020)$ resonance, using 6 fb$^{-1}$ of LHCb data at 13 TeV.

Contribution

It provides new, highly precise measurements of $CP$ violation parameters in $B^0_s$ decays, including $_s$, $ riangle ext{ extGamma}_s$, and $ ext{ extGamma}_s - ext{ extGamma}_d$, consistent with the Standard Model.

Findings

Measured $_s = -0.039 ext{ rad}$ with uncertainties

Measured $ riangle ext{ extGamma}_s = 0.0845 ext{ ps}^{-1}$ with uncertainties

Results are the most precise to date and agree with Standard Model expectations

Abstract

The decay-time-dependent $CP$ asymmetry in $B^0_s\to J/\psi(\to \mu^{+}\mu^{-}) K^{+}K^{-}$ decays is measured using proton-proton collision data, corresponding to an integrated luminosity of 6 $fb^{-1}$, collected with the LHCb detector at a center-of-mass energy of 13 TeV. Using a sample of approximately 349 000 $B^{0}_{s}$ signal decays with an invariant $K^{+}K^{-}$ mass in the vicinity of the $\phi(1020)$ resonance, the $CP$-violating phase $\phi_s$ is measured, along with the difference in decay widths of the light and heavy mass eigenstates of the $B^0_s$-$\bar{B}^0_s$ system, $\Delta\Gamma_s$, and the difference of the average $B^0_s$ and $B^0$ meson decay widths, $\Gamma_s-\Gamma_d$. The values obtained are $\phi_s = \ -0.039 \pm 0.022 \pm 0.006$ rad, $\Delta\Gamma_s = 0.0845 \pm 0.0044 \pm 0.0024 $ ps$^{-1}$ and $\Gamma_s-\Gamma_d = -0.0056 ^{+ 0.0013}_{-0.0015} \pm 0.0014$ ps$^{-1}$, where the first uncertainty is statistical and the second systematic. These are the most precise single measurements to date and are consistent with expectations based on the Standard Model and with the previous LHCb analyses of this decay. These results are combined with previous independent LHCb measurements. The phase $\phi_s$ is also measured independently for each polarization state of the $K^{+}K^{-}$ system and shows no evidence for polarization dependence.